1/*
  2 * Copyright (C) 2014 Linaro Ltd. <ard.biesheuvel@linaro.org>
  3 *
  4 * This program is free software; you can redistribute it and/or modify
  5 * it under the terms of the GNU General Public License version 2 as
  6 * published by the Free Software Foundation.
  7 */
  8
  9#include <linux/elf.h>
 10#include <linux/kernel.h>
 11#include <linux/module.h>
 12
 13#include <asm/cache.h>
 14#include <asm/opcodes.h>
 15
 16#define PLT_ENT_STRIDE		L1_CACHE_BYTES
 17#define PLT_ENT_COUNT		(PLT_ENT_STRIDE / sizeof(u32))
 18#define PLT_ENT_SIZE		(sizeof(struct plt_entries) / PLT_ENT_COUNT)
 19
 20#ifdef CONFIG_THUMB2_KERNEL
 21#define PLT_ENT_LDR		__opcode_to_mem_thumb32(0xf8dff000 | \
 22							(PLT_ENT_STRIDE - 4))
 23#else
 24#define PLT_ENT_LDR		__opcode_to_mem_arm(0xe59ff000 | \
 25						    (PLT_ENT_STRIDE - 8))
 26#endif
 27
 28struct plt_entries {
 29	u32	ldr[PLT_ENT_COUNT];
 30	u32	lit[PLT_ENT_COUNT];
 31};
 32
 33static bool in_init(const struct module *mod, u32 addr)
 34{
 35	return addr - (u32)mod->init_layout.base < mod->init_layout.size;
 36}
 37
 38u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
 39{
 40	struct plt_entries *plt, *plt_end;
 41	int c, *count;
 42
 43	if (in_init(mod, loc)) {
 44		plt = (void *)mod->arch.init_plt->sh_addr;
 45		plt_end = (void *)plt + mod->arch.init_plt->sh_size;
 46		count = &mod->arch.init_plt_count;
 47	} else {
 48		plt = (void *)mod->arch.core_plt->sh_addr;
 49		plt_end = (void *)plt + mod->arch.core_plt->sh_size;
 50		count = &mod->arch.core_plt_count;
 51	}
 52
 53	/* Look for an existing entry pointing to 'val' */
 54	for (c = *count; plt < plt_end; c -= PLT_ENT_COUNT, plt++) {
 55		int i;
 56
 57		if (!c) {
 58			/* Populate a new set of entries */
 59			*plt = (struct plt_entries){
 60				{ [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
 61				{ val, }
 62			};
 63			++*count;
 64			return (u32)plt->ldr;
 65		}
 66		for (i = 0; i < PLT_ENT_COUNT; i++) {
 67			if (!plt->lit[i]) {
 68				plt->lit[i] = val;
 69				++*count;
 70			}
 71			if (plt->lit[i] == val)
 72				return (u32)&plt->ldr[i];
 73		}
 74	}
 75	BUG();
 76}
 77
 78static int duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num,
 79			   u32 mask)
 80{
 81	u32 *loc1, *loc2;
 82	int i;
 83
 84	for (i = 0; i < num; i++) {
 85		if (rel[i].r_info != rel[num].r_info)
 86			continue;
 87
 88		/*
 89		 * Identical relocation types against identical symbols can
 90		 * still result in different PLT entries if the addend in the
 91		 * place is different. So resolve the target of the relocation
 92		 * to compare the values.
 93		 */
 94		loc1 = (u32 *)(base + rel[i].r_offset);
 95		loc2 = (u32 *)(base + rel[num].r_offset);
 96		if (((*loc1 ^ *loc2) & mask) == 0)
 97			return 1;
 98	}
 99	return 0;
100}
101
102/* Count how many PLT entries we may need */
103static unsigned int count_plts(Elf32_Addr base, const Elf32_Rel *rel, int num)
104{
105	unsigned int ret = 0;
106	int i;
107
108	/*
109	 * Sure, this is order(n^2), but it's usually short, and not
110	 * time critical
111	 */
112	for (i = 0; i < num; i++)
113		switch (ELF32_R_TYPE(rel[i].r_info)) {
114		case R_ARM_CALL:
115		case R_ARM_PC24:
116		case R_ARM_JUMP24:
117			if (!duplicate_rel(base, rel, i,
118					   __opcode_to_mem_arm(0x00ffffff)))
119				ret++;
120			break;
121#ifdef CONFIG_THUMB2_KERNEL
122		case R_ARM_THM_CALL:
123		case R_ARM_THM_JUMP24:
124			if (!duplicate_rel(base, rel, i,
125					   __opcode_to_mem_thumb32(0x07ff2fff)))
126				ret++;
127#endif
128		}
129	return ret;
130}
131
132int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
133			      char *secstrings, struct module *mod)
134{
135	unsigned long core_plts = 0, init_plts = 0;
136	Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
137
138	/*
139	 * To store the PLTs, we expand the .text section for core module code
140	 * and the .init.text section for initialization code.
141	 */
142	for (s = sechdrs; s < sechdrs_end; ++s)
143		if (strcmp(".core.plt", secstrings + s->sh_name) == 0)
144			mod->arch.core_plt = s;
145		else if (strcmp(".init.plt", secstrings + s->sh_name) == 0)
146			mod->arch.init_plt = s;
147
148	if (!mod->arch.core_plt || !mod->arch.init_plt) {
149		pr_err("%s: sections missing\n", mod->name);
150		return -ENOEXEC;
151	}
152
153	for (s = sechdrs + 1; s < sechdrs_end; ++s) {
154		const Elf32_Rel *rels = (void *)ehdr + s->sh_offset;
155		int numrels = s->sh_size / sizeof(Elf32_Rel);
156		Elf32_Shdr *dstsec = sechdrs + s->sh_info;
157
158		if (s->sh_type != SHT_REL)
159			continue;
160
161		if (strstr(secstrings + s->sh_name, ".init"))
162			init_plts += count_plts(dstsec->sh_addr, rels, numrels);
163		else
164			core_plts += count_plts(dstsec->sh_addr, rels, numrels);
165	}
166
167	mod->arch.core_plt->sh_type = SHT_NOBITS;
168	mod->arch.core_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
169	mod->arch.core_plt->sh_addralign = L1_CACHE_BYTES;
170	mod->arch.core_plt->sh_size = round_up(core_plts * PLT_ENT_SIZE,
171					       sizeof(struct plt_entries));
172	mod->arch.core_plt_count = 0;
173
174	mod->arch.init_plt->sh_type = SHT_NOBITS;
175	mod->arch.init_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
176	mod->arch.init_plt->sh_addralign = L1_CACHE_BYTES;
177	mod->arch.init_plt->sh_size = round_up(init_plts * PLT_ENT_SIZE,
178					       sizeof(struct plt_entries));
179	mod->arch.init_plt_count = 0;
180	pr_debug("%s: core.plt=%x, init.plt=%x\n", __func__,
181		 mod->arch.core_plt->sh_size, mod->arch.init_plt->sh_size);
182	return 0;
183}